JPH0673887B2 - Injection molding mold and method of molding disk substrate using the mold - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a mold for injection molding of plastic molded products and a method for molding a disc substrate using the mold.

[Prior Art] Generally, an injection molding method is used for molding an optical disk substrate, a video disk substrate and the like. According to the conventional injection molding method using a mold for injection molding, at the time of injection molding, a heat medium having a predetermined temperature, for example, in a heat medium flow path formed in each of the movable mold and the fixed mold along the cavity is formed. Pour water,
The molten resin injected into the cavity and the molten resin in the sprue are cooled and solidified.

[Problems to be Solved by the Invention] In the injection molding method, the temperature of water flowing in the heat medium passage formed in the vicinity of the outer periphery of the sprue is set to a low temperature (for example, 10 to 40).
(° C), the molten resin in the sprue is also rapidly cooled and solidified, so that the molding cycle can be shortened. However, on the contrary, since the temperature distribution in the inner and outer peripheral parts of the resin cooled in the cavity becomes non-uniform,
The birefringence distribution of the obtained substrate varies and warpage occurs, which causes problems with respect to optical properties and mechanical properties. Further, since the outer periphery of the sprue is cooled, the mold temperature of the gate portion is also relatively low, the injected resin is cooled, and the pressure rise of the gate portion due to the increase in viscosity causes a silver streak. .

On the other hand, the temperature of the water flowing in the heat medium passage is set to a high temperature (for example, 50 to 90
C.), the temperature distribution in the inner and outer peripheral portions of the resin cooled in the cavity is made uniform, so that it is possible to obtain a substrate having both excellent optical characteristics and mechanical characteristics. However, for the molten resin in the sprue, the cooling and solidification of the resin becomes slow, so not only the cycle time becomes long, but also mold release failure easily occurs due to insufficient cooling of the sprue, which makes continuous molding of the substrate impossible. The problem arises.

Incidentally, Japanese Patent Laid-Open No. 61-217225 discloses an injection molding die in which a means for heating the sprue and a means for cooling the sprue are provided in the vicinity of the sprue. But,
According to this configuration, i. The switching operation between heating and cooling is required, and the response at that time is slow, and the molding cycle becomes long, which is disadvantageous to continuous production. ii. It is difficult to control and stabilize the temperature. iii. Since the temperature of the entire sprue bush including the center of the substrate is cooled uniformly, the resin is cooled too much and it becomes difficult to form the center hole. Is accompanied by.

The present invention provides a mold for injection molding capable of obtaining a molded product having good optical properties and mechanical properties and shortening the molding cycle, and a method of molding a disk substrate using this mold. To aim.

MEANS FOR SOLVING THE PROBLEM The present invention is to introduce a cavity into the abutting surface of a fixed die and a movable die, a sprue into which a resin is melt-injected, and introduce the resin into the cavity from the sprue. An injection-molding die having a gate portion, comprising: a first temperature control means for cooling, provided near the sprue; and a second temperature control means for keeping heat, provided near the gate portion. It is characterized by that.

The first temperature control means for cooling provided in the vicinity of the sprue is constituted by, for example, as a heat medium passage, by flowing a heat medium such as water having a predetermined temperature therethrough, or a heating and cooling element such as a Peltier effect element. Can be arranged and configured.

Further, the second temperature control means for keeping heat provided near the gate portion is, for example, as a heat medium flow path, a heat medium such as water having a predetermined temperature is allowed to flow therein, or a heat absorbing element is arranged,
Alternatively, a heat insulating layer is formed between the sprue portion and a temperature control means provided near the sprue portion so that the gate portion is not cooled by cooling the sprue portion. Here, the heat insulating layer can be formed by interposing a layer of a material having a low thermal conductivity such as air, glass balloons or various foams.

The plastic molded product molded by this injection molding die is not particularly limited and may be, for example, an optical disk substrate, a video disk substrate, an eyeglass lens, or the like, but a molded product for an optical member is particularly preferable.

Further, the present invention uses the above-mentioned injection molding die, and a disk substrate for injecting a molten resin from a sprue through a gate portion into a disk-shaped cavity formed on a butting surface of a fixed die and a movable die. In the molding method, the temperature control for cooling the sprue by the first temperature control means provided in the vicinity of the sprue and the temperature control for maintaining the temperature of the gate portion by the second temperature control means provided in the vicinity of the gate portion are independent of each other. It is characterized in that

Here, in the case of molding a polycarbonate resin optical disk substrate [for example, thickness 1.2 mm, diameter 130 mm], for example, the first temperature control means provided in the vicinity of the sprue is used as the heat medium flow path, and the heat medium is placed at 20 to 70 / It is suitable to flow it at a flow rate of min and set its temperature to 20-40 ° C.

When the second temperature control means provided in the vicinity of the gate portion is used as a heat medium flow path and the heat medium is made to flow there, the temperature of the heat medium is set to 40 ° C. or higher, preferably 80 to 130 ° C.
And A suitable flow rate of the heat medium is 20 to 70 / min.

Next, changing to the heat medium flow path of the second temperature control means,
When the structure having the heat insulating layer is formed, the vicinity of the gate portion is less affected by being cooled by the first temperature control means, and is usually kept at 80 ° C. or higher by the flow of the high temperature resin. In addition, in the present invention, forming control becomes more possible by adopting the two configurations of forming the heat insulating layer and providing the heat medium flow passage.

The resin melt-injected from the sprue has a temperature of 310-350 ° C.
And a pressure of 250 to 350 kg / cm ² is suitable.

The heat medium flowing through the heat medium flow paths formed in the movable mold and the fixed mold along the cavity, respectively, has a temperature of 100 to 130 ° C. and a flow rate of 20 to 70 / min. Also,
The cooling time of the molten resin injected into the cavity is 10-18
Seconds are appropriate.

Water or the like can be used as the heat medium flowing through the heat medium flow path.

The molding resin used is polycarbonate resin (Mv: 120
00 to 18000) is preferable, but acrylic resin, amorphous polyolefin, etc. are optional.

In the present invention, injection molding includes the case of injection compression molding.

[Operation] According to the molding method of the present invention, the first temperature control means is provided in the vicinity of the sprue, and the second temperature control means is provided in the vicinity of the gate portion.
The temperature control means for cooling the outer circumference of the sprue and the second temperature control means provided near the gate portion keep the temperature near the gate portion, so that different temperature controls can be independently performed. As a result, the resin injected into the cavity is filled in the cavity without being cooled in the gate portion, so that the temperature distribution of the resin in the inner and outer peripheral portions of the substrate becomes uniform, and good optical and mechanical characteristics are achieved. A substrate is obtained. At the same time, after injection molding, the molten resin in the sprue is quickly cooled and solidified, so that the molding cycle can be shortened.

[Embodiment] With reference to FIG. 1, an injection molding die according to an embodiment of the present invention and a method of molding a disk substrate using this die will be described.

This injection molding die has a fixed die 2 attached to a fixed die plate 1 and a movable die 4 attached to a movable die plate 3, and these are fixed via spacers 16 and 17. The disk-shaped gap formed on the surface where the mold 2 and the movable mold 4 are abutted with each other becomes a cavity 5 for molding an optical disk substrate or the like.

A cylindrical sprue bush 6 is provided at the center of the fixed mold 2.
To form a sprue 7 along which the molten resin is injected along the center line of the sprue bush 6. A plurality of annular heat medium flow passages 15 are formed in the fixed mold 2 at appropriate distances from the cavity 5.

A cylindrical center member 8 is embedded in the center of the other movable mold 4, and a cut pin 9 is arranged along the center line of the center member 8. On the inner mirror surface of the movable mold 4, there is provided a stamper 10 having pits, grooves, etc., which will be record carriers,
This stamper 10 is fixed with a stamper holder 11.
In addition, a plurality of annular heat medium flow paths 15 are formed in the movable mold 4 at appropriate distances from the cavity 5.

When the fixed mold 2 and the movable mold 4 are butted against each other, the gap formed by the sprue bush 6 and the center member 8 becomes a gate portion 12 for introducing the molten resin from the sprue 7 into the cavity 5.

Then, a first annular heat medium passage 13 which is a first temperature control means for cooling is provided in the sprue bush 6 at a position near the sprue 7 and away from the gate portion 12 so as to surround the outer periphery of the sprue 7. At the same time as the formation, the second annular heat medium flow passage 14 which is the second temperature control means for keeping heat is formed in the sprue bush 6 near the gate portion 12. In addition, a third annular heat medium flow passage 13A for cooling is formed in the center member 8 in the vicinity of the cut pin 9 and away from the gate portion 12, and a heat insulating first annular heat medium passage 13A is formed in the vicinity of the gate portion 12. The four annular heat medium flow paths 14A are formed.

Next, a method of molding an optical disk substrate using the injection molding die will be described.

As shown in FIG. 1, the fixed mold 2 and the movable mold 4 are abutted against each other, and the heat medium flow path 15 of the fixed mold 2 and the movable mold 4 is
Flow pressurized water at 0 ℃ at a flow rate of 40 / min. Water of 80 ° C. is flown at a flow rate of 40 / min through the second and fourth heat medium flow passages 14 and 14A of the sprue bush 6 and the center member 8.

Then, the melted polycarbonate resin of 330 ° C (Mv: 14
800) is injected from the injection cylinder 17 into the sprue 7 at a pressure of 300 kg / cm ² , and this molten resin is introduced into the cavity 5 through the gate portion 12. The molten resin injected into the cavity 5 is a heat medium flow path of the fixed mold 2 and the movable mold 4.
It is cooled and solidified in 12.5 seconds by pressurized water flowing in 15.

On the other hand, the molten resin in the sprue 7 is cooled and solidified by constantly flowing water at 35 ° C. at a flow rate of 40 / min through the first and third heat medium flow passages 13 and 13A of the sprue bush 6 and the center member 8. .

Regarding the optical disk substrate obtained by the above molding method,
The results of measuring the birefringence before heat treatment and after heat treatment at 80 ° C. for 2 hours are shown in FIG. In the figure, curve A is the birefringence before heat treatment, and curve B is the birefringence after heat treatment.

Further, as a comparative example, an optical disk substrate was prepared in the same manner as in the above-mentioned embodiment by using an injection molding die in which the second and fourth heat medium passages 14 and 14A were not formed in the spool bush 6 and the center member 8. Injection molded. Similarly, the results of measuring the birefringence of this optical disk substrate before and after the heat treatment are shown in FIG. In the figure, curve C is the birefringence before heat treatment, and curve D is the birefringence after heat treatment.

From the curve A in FIG. 2, in the case of the optical disc substrate before the heat treatment according to the example, the temperature distribution of the resin injected into the cavity 5 by the second heat medium flow passage 14 was made uniform, so that the dispersion of the birefringence was small. , Was kept within ± 10 nm (double pass), and was substantially uniform from the inner peripheral portion to the outer peripheral portion of the substrate.

Also, from curves A and B, the change in birefringence before heat treatment and after heat treatment at 80 ° C. for 2 hours shows that the temperature distribution of the resin in the cavity 5 becomes uniform and the thermal stress is reduced.
(Double pass) The amount of change was less than the following.

Furthermore, the change in birefringence with time hardly changed even after 1 week at room temperature.

On the other hand, according to the curve C in FIG. 3, in the case of the optical disc substrate before the heat treatment according to the comparative example, the birefringence of the inner peripheral portion is +32 nm.
(Double pass), the birefringence of the outer peripheral part is -20 nm (double pass), the radial variation is extremely large, and it can be seen that the optical characteristics are poor.

Also, from curves C and D, the change in birefringence before heat treatment and after heat treatment at 80 ° C for 2 hours shows that the temperature distribution of the resin in the cavity is not uniform and the thermal stress is high. Is 40-50
It was very large with nm (double pass).

Further, with respect to the change with time of the birefringence, a change amount of 5 to 10 nm (double pass) was observed at the inner peripheral portion after 24 hours at room temperature.

Next, the mechanical characteristics of the optical disk substrates according to these examples and comparative examples were measured. The measurement of the mechanical characteristics is performed for warpage, surface wobbling, skew angle, and surface wobbling acceleration. The measurement results are shown in Table 1 below.

From the measurement results, the optical disk substrate of the example has smaller mechanical warp, surface wobbling, skew angle, and surface wobbling acceleration than the optical disk substrate of the comparative example, and has good mechanical characteristics. I understand.

Further, according to the present embodiment, the molten resin in the sprue 7 is rapidly cooled and solidified by the first heat medium passage 13 formed in the sprue bush 6 in the vicinity of the sprue 7, so that the molding time is shortened. The effect was also obtained. Also, the first
Since the heat medium having a constant temperature is constantly flowing in the heat medium flow passage of No. 3, the temperature of the injection resin is constant, and the performance of the molded disk substrate is stable and stable.

Furthermore, since the pressure rise at the gate portion 12 was small, no silver streak was observed.

In the above embodiment, the third heat medium passage 13A for cooling and the fourth heat medium passage 14A for keeping heat are formed in the center member 8 as well, but these are not provided. The first heat medium flow passage 13 and the second heat medium flow passage 14 may be formed only in the sprue bush 6.

EFFECTS OF THE INVENTION According to the injection molding die of the present invention, a plastic molded product having excellent optical characteristics and mechanical characteristics can be obtained, and the molding cycle can be shortened. Then, according to the method of molding a disk substrate using this mold, it is possible to obtain a disk substrate having a small variation in birefringence and a change with time, and good mechanical characteristics such as warpage and surface wobbling.

[Brief description of drawings]

1 is a cross-sectional view of an injection molding die according to an embodiment of the present invention, FIG. 2 is a graph showing birefringence of an optical disk substrate according to the embodiment before and after heat treatment, and FIG. 3 is a comparative example. 6 is a graph in which the birefringence of the optical disc substrate according to FIG. 2 ... Fixed mold, 4 ... Movable mold, 5 ... Cavity,
6 ... Sprue bush, 7 ... Sprue, 12 ... Gate part, 13 ... First heat medium flow passage, 14 ... Second heat medium flow passage.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-57-64531 (JP, A) JP-A-57-203530 (JP, A) JP-A-61-3716 (JP, A) Actual development Sho-61- 8115 (JP, U)

Claims (2)

[Claims] 1. A mold for injection molding, comprising a cavity formed on an abutting surface of a fixed mold and a movable mold, a sprue for melting and injecting a resin, and a gate portion for introducing the resin into the cavity from the sprue. The injection molding is characterized in that the mold comprises a first temperature control means for cooling provided near the sprue and a second temperature control means for heat retention provided near the gate portion. Mold for. 2. Using the injection molding die according to claim 1, molten resin is spun from a sprue through a gate into a disk-shaped cavity formed on the abutting surface of a fixed die and a movable die. In a method of molding a disk substrate for injection, temperature control for cooling the sprue by a first temperature control means provided in the vicinity of the sprue and heat retention of the gate portion by a second temperature control means provided in the vicinity of the gate portion. A method of molding a disk substrate, wherein the temperature control is performed independently of each other.